Dual metal capped via contact structures for semiconductor devices

ABSTRACT

The structure of a semiconductor device with dual metal capped via contact structures and a method of fabricating the semiconductor device are disclosed. A method of fabricating the semiconductor device includes forming a source/drain (S/D) region and a gate structure on a fin structure, forming S/D and gate contact structures on the S/D region and the gate structure, respectively, forming first and second via contact structures on the S/D and gate contact structures, respectively, and forming first and second interconnect structures on the first and second via contact structures, respectively. The forming of the first and second via contact structures includes forming a first via contact plug interposed between first top and bottom metal capping layers and a second via contact plug interposed between second top and bottom metal capping layers, respectively.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 16/692,127, filed on Nov. 22, 2019, titled “DualMetal Capped Via Contact Structures For Semiconductor Devices,” which isincorporated herein by reference in its entirety.

BACKGROUND

With advances in semiconductor technology, there has been increasingdemand for higher storage capacity, faster processing systems, higherperformance, and lower costs. To meet these demands, the semiconductorindustry continues to scale down the dimensions of semiconductordevices, such as metal oxide semiconductor field effect transistors(MOSFETs), including planar MOSFETs and fin field effect transistors(finFETs). Such scaling down has increased the complexity ofsemiconductor manufacturing processes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of this disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the common practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates an isometric view of a semiconductor device, inaccordance with some embodiments.

FIG. 2 illustrates a cross-sectional view of a semiconductor device, inaccordance with some embodiments.

FIG. 3 is a flow diagram of a method for fabricating a semiconductordevice with via contact structures, in accordance with some embodiments.

FIGS. 4-13 illustrate cross-sectional views of a semiconductor device atvarious stages of its fabrication process, in accordance with someembodiments.

Illustrative embodiments will now be described with reference to theaccompanying drawings. In the drawings, like reference numeralsgenerally indicate identical, functionally similar, and/or structurallysimilar elements.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over a second feature in the description that followsmay include embodiments in which the first and second features areformed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Asused herein, the formation of a first feature on a second feature meansthe first feature is formed in direct contact with the second feature.In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition does not in itselfdictate a relationship between the various embodiments and/orconfigurations discussed.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. The spatially relative termsare intended to encompass different orientations of the device in use oroperation in addition to the orientation depicted in the figures. Theapparatus may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein maylikewise be interpreted accordingly.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “exemplary,” etc., indicatethat the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of oneskilled in the art to effect such feature, structure or characteristicin connection with other embodiments whether or not explicitlydescribed.

It is to be understood that the phraseology or terminology herein is forthe purpose of description and not of limitation, such that theterminology or phraseology of the present specification is to beinterpreted by those skilled in relevant art(s) in light of theteachings herein.

As used herein, the term “etch selectivity” refers to the ratio of theetch rates of two different materials under the same etching conditions.

As used herein, the term “deposition selectivity” refers to the ratio ofthe deposition rates on two different materials or surfaces under thesame deposition conditions.

As used herein, the term “substrate” describes a material onto whichsubsequent material layers are added. The substrate itself may bepatterned. Materials added on top of the substrate may be patterned ormay remain unpatterned. Furthermore, the substrate may be a wide arrayof semiconductor materials such as, for example, silicon, germanium,gallium arsenide, indium phosphide, etc. Alternatively, the substratemay be made from an electrically non-conductive material such as, forexample, a glass or a sapphire wafer.

As used herein, the term “high-k” refers to a high dielectric constant.In the field of semiconductor device structures and manufacturingprocesses, high-k refers to a dielectric constant that is greater thanthe dielectric constant of SiO₂ (e.g., greater than 3.9).

As used herein, the term “low-k” refers to a small dielectric constant.In the field of semiconductor device structures and manufacturingprocesses, low-k refers to a dielectric constant that is less than thedielectric constant of SiO₂ (e.g., less than 3.9).

As used herein, the term “p-type” defines a structure, layer, and/orregion as being doped with p-type dopants, such as, for example, boron.

As used herein, the term “n-type” defines a structure, layer, and/orregion as being doped with n-type dopants, such as, for example,phosphorus.

As used herein, the term “vertical” means nominally perpendicular to thesurface of a substrate.

In some embodiments, the terms “about” and “substantially” can indicatea value of a given quantity that varies within 5% of the value (e.g.,±1%, ±2%, ±3%, ±4%, ±5% of the value).

The fin structures discloses herein may be patterned by any suitablemethod. For example, the fin structures may be patterned using one ormore photolithography processes, including double-patterning ormulti-patterning processes. Generally, double-patterning ormulti-patterning processes combine photolithography and self-alignedprocesses, allowing patterns to be created that have, for example,pitches smaller than what is otherwise obtainable using a single, directphotolithography process. For example, in one embodiment, a sacrificiallayer is formed over a substrate and patterned using a photolithographyprocess. Spacers are formed alongside the patterned sacrificial layerusing a self-aligned process. The sacrificial layer is then removed, andthe remaining spacers may then be used to pattern the fin structures.

The present disclosure provides example via contact structures with dualmetal capping layers (also referred to as dual metal capped via contactstructures) in field effect transistors (FET) devices (e.g., finFETs,gate-all-around FETs, MOSFETs, etc.) and/or other semiconductor devicesin an integrated circuit (IC) and example methods for fabricating thesame. The dual metal capped via contact structures on source/drainand/or gate contact structures can reduce the contact resistance betweensemiconductor devices and interconnect structures (e.g., conductivelines, vias structures, etc.), thus resulting in improved deviceperformance compared to semiconductor devices without dual metal cappedvia contact structures. The upper metal capping layers (e.g., tungsten(W) capping layers) of the dual metal capping layers can reduceelectromigration of materials (e.g., copper (Cu)) from interconnectstructures overlying the via contact structures and improve yield of thesemiconductor devices. The bottom metal capping layers (e.g., tungsten(W) capping layers) of the dual metal capping layers can preventcorrosions of underlying source/drain and/or gate contact structuresduring subsequent processes.

The scaling down of FET devices has increased the complexity offabricating via contact structures with low resistivity in via contactopenings with dimensions (e.g., width or diameter) less than about 20nm. The resistance of tungsten (W) via contact structures with liners asadhesion layer can be high for via contact structures with such smalldimensions. One of the challenges of fabricating via contact structureswith such small dimensions can be the fabrication of void-free viacontact structures. The presence of voids in via contact structures canincrease their resistivity, and as a result increase the contactresistance between the semiconductor devices and interconnectstructures.

The example structures and methods disclosed herein providesubstantially void-free (e.g., with no voids) dual metal capped viacontact structures. The substantially void-free dual metal capped viacontact structures can be formed with low resistivity in via contactopenings with dimensions (e.g., width or diameter) less than about 20 nmand with high aspect ratio (e.g., about 5 to about 8). The aspect ratioof the via contact openings can be a ratio of their vertical dimensions(e.g., height) to their horizontal dimensions (e.g., width or diameter).

In some embodiments, the dual metal capped via contact structures caninclude via contact plugs having one or more metal layers of lowresistivity metals, such as ruthenium (Ru), iridium (Ir), nickel (Ni),Osmium (Os), rhodium (Rh), aluminum (Al), molybdenum (Mo), tungsten (W),or cobalt (Co), and/or other suitable low resistivity metals, and topand bottom metal capping layers disposed on top and bottom surfaces ofthe via contact plugs, where the top and bottom metal capping layersinclude low resistivity metals different from the via contact plugs. Insome embodiments, dual metal capped via contact structures with Ru-basedvia contact plugs, with dimensions ranging from about 10 nm to about 15nm, and with aspect ratios ranging from about 5 to about 8 has lowerresistivity compared to via contact structures with Cu, W, or Co-basedvia contact plugs and similar dimensions. In some embodiments, theRu-based dual metal capped via contact structures can reduce via contactresistance by about 10% to about 30% compared to W, Cu, or Co-based viacontact structures with similar dimensions.

In some embodiments, the dual metal capped via contact structures can beformed without metal-based barrier layers (also referred to as adhesionlayers or liners) along the sidewalls of via contact openings. As themetal(s) of the via contact plugs can have lower resistivity than themetal-based barrier layers, the resistance of the via contact structurescan be reduced without the metal-based barrier layers.

Though the present disclosure describes the dual metal capped viacontact structures on source/drain (S/D) and/or gate contact structuresof a finFET, the dual metal capped via contact structures and themethods for forming these structures described herein can be applied toother FETs and other semiconductor devices, such as gate-all-around(GAA) FETs, MOSFETs, high resistance resistors, or passive devices.

FIG. 1 illustrates an isometric view of a semiconductor device 100,according to some embodiments. The isometric view of semiconductordevice 100 is shown for illustration purposes and may not be drawn toscale. Semiconductor device 100 can be formed on a substrate 102 and caninclude fin structures 104, gate structures 108 disposed on finstructures 104, spacers 110 disposed on opposite sides of gatestructures 108, and shallow trench isolation (STI) regions 112. ThoughFIG. 1 shows five gate structures 108, semiconductor device 100 caninclude one or more gate structures similar and parallel to gatestructures 108.

Substrate 102 can be a semiconductor material such as, but not limitedto, silicon. In some embodiments, substrate 102 includes a crystallinesilicon substrate (e.g., wafer). In some embodiments, substrate 102includes (i) an elementary semiconductor, such as germanium; (ii) acompound semiconductor including silicon carbide, gallium arsenide,gallium phosphide, indium phosphide, indium arsenide, and/or indiumantimonide; (iii) an alloy semiconductor including silicon germaniumcarbide, silicon germanium, gallium arsenic phosphide, gallium indiumphosphide, gallium indium arsenide, gallium indium arsenic phosphide,aluminum indium arsenide, and/or aluminum gallium arsenide; or (iv) acombination thereof. Further, substrate 102 can be doped depending ondesign requirements (e.g., p-type substrate or n-type substrate). Insome embodiments, substrate 102 can be doped with p-type dopants (e.g.,boron, indium, aluminum, or gallium) or n-type dopants (e.g., phosphorusor arsenic).

Fin structures 104 represent current carrying structures ofsemiconductor device 100 and can traverse along an X-axis and throughgate structures 108. Fin structures 104 can include: (i) epitaxial finregions 105 disposed on opposing sides of gate structures 108; and (ii)fin regions 106 underlying epitaxial fin regions 105 and gate structures108. Epitaxial fin regions 105 can form source/drain (S/D) regions ofsemiconductor device 100 and the portions of fin regions 106 underlyinggate structures 108 can form the channel regions (not shown) ofsemiconductor device 100. Fin regions 106 can be formed from patternedportions of substrate 102 and form interfaces 121 with epitaxial finregions 105. In some embodiments, interfaces 121 can be coplanar withtop surface of STI regions 112 or top surface of substrate 102. Thoughsemiconductor device 100 is shown to have merged epitaxial fin region105 on three fin regions 106, semiconductor device 100 can have anindividual epitaxial fin region similar in composition to epitaxial finregion 105 on each fin region 106.

Each of epitaxial fin regions 105 can include an epitaxially-grownsemiconductor material. In some embodiments, the epitaxially grownsemiconductor material is the same material as the material of substrate102. In some embodiments, the epitaxially-grown semiconductor materialcan include a different material from the material of substrate 102. Theepitaxially-grown semiconductor material can include: (i) asemiconductor material, such as germanium or silicon; (ii) a compoundsemiconductor material, such as gallium arsenide and/or aluminum galliumarsenide; or (iii) a semiconductor alloy, such as silicon germaniumand/or gallium arsenide phosphide.

In some embodiments, epitaxial fin regions 105 can be grown by (i)chemical vapor deposition (CVD), such as low pressure CVD (LPCVD),atomic layer CVD (ALCVD), ultrahigh vacuum CVD (UHVCVD), reducedpressure CVD (RPCVD), or any suitable CVD; (ii) molecular beam epitaxy(MBE) processes; (iii) any suitable epitaxial process; or (iv) acombination thereof. In some embodiments, epitaxial fin regions 105 canbe grown by an epitaxial deposition/partial etch process, which repeatsthe epitaxial deposition/partial etch process at least once. Suchrepeated deposition/partial etch process is also called a cyclicdeposition-etch (CDE) process. In some embodiments, epitaxial finregions 105 can be grown by selective epitaxial growth (SEG), where anetching gas is added to promote the selective growth of semiconductormaterial on the exposed surfaces of fin regions 106, but not oninsulating material (e.g., dielectric material of STI regions 112).

Each of epitaxial fin regions 105 can be p-type or n-type. Each ofp-type epitaxial fin regions 105 can include SiGe, Si, silicon germaniumbromide (SiGeB), Ge or III-V materials (e.g., indium antimonide (InSb),gallium antimonide (GaSb), or indium gallium antimonide (InGaSb)) andcan be in-situ doped during an epitaxial growth process using p-typedopants, such as boron, indium, or gallium. For p-type in-situ doping,p-type doping precursors, such as diborane (B₂H₆), boron trifluoride(BF₃), and/or other p-type doping precursors, can be used.

Each of p-type epitaxial fin regions 105 can include epitaxially grownp-type first, second, and third sub-regions (not shown), where the thirdsub-region can be grown on the second sub-region, and the secondsub-region can be grown on the first sub-region. In some embodiments,the sub-regions can have SiGe and differ from each other based on, forexample, doping concentration, epitaxial growth process conditions,and/or relative concentration of Ge with respect to Si. For example, theatomic percent Ge in the first sub-region can be less than the atomicpercent Ge in the second sub-region and greater than the atomic percentGe in third sub-region. In some embodiments, the atomic percent Ge inthe first sub-region can be equal to the atomic percent Ge in the secondsub-region, but greater than the atomic percent Ge in the thirdsub-region. In some embodiments, the first sub-region can include Ge ina range from about 15 atomic percent to about 35 atomic percent, whilethe second sub-region can include Ge in a range from about 35 atomicpercent to about 70 atomic percent and the third sub-region can includeless than about 25 atomic percent Ge with any remaining atomic percentbeing Si in the sub-regions.

The sub-regions can be epitaxially grown under a pressure of about 10Torr to about 300 Torr, at a temperature from about 500° C. to about700° C. using reaction gases, such as HCl as an etching agent, GeH₄ asGe precursor, dichlorosilane (DCS) and/or SiH₄ as Si precursor, B₂H₆ asB dopant precursor, H₂, and/or N₂. To achieve different concentration ofGe in the sub-regions, the ratio of a flow rate of Ge to Si precursorsmay be varied during their respective growth process. For example, a Geto Si precursor flow rate ratio in a range from about 9 to about 25 canbe used during the epitaxial growth of the second sub-region, while a Geto Si precursor flow rate ratio less than about 6 can be used during theepitaxial growth of the third sub-region.

The sub-regions can have varying dopant concentration with respect toeach other. For example, the first sub-region can be undoped or can havea dopant concentration lower than the dopant concentrations of thesecond and third sub-regions. In some embodiments, the first sub-regioncan have a dopant concentration less than about 5×10²⁰ atoms/cm³, whilethe second sub-region can have a dopant concentration in a range fromabout 1×10²⁰ to about 2×10²¹ atoms/cm³ and the third sub-region can havea dopant concentration in a range from about 1×10²⁰ to about 3×10²¹atoms/cm³.

In some embodiments, each of n-type epitaxial fin regions 105 caninclude Si, silicon phosphide (SiP), silicon carbide (SiC), siliconphosphorus carbide (SiPC), or III-V materials (e.g., indium phosphide(InP), gallium arsenide (GaAs), aluminum arsenide (AlAs), indiumarsenide (InAs), indium aluminum arsenide (InAlAs), or indium galliumarsenide (InGaAs)) and can be in-situ doped during an epitaxial growthprocess using n-type dopants, such as phosphorus or arsenic. For n-typein-situ doping, n-type doping precursors, such as phosphine (PH₃),arsine (AsH₃), and/or other n-type doping precursor, can be used. Eachof epitaxial fin regions 105 can have multiple n-type sub-regions.Except for the type of dopants, the n-type sub-regions can be similar tothe p-type sub-regions, in thickness, dopant concentration, and/orepitaxial growth process conditions. Other materials, thicknesses, anddopant concentrations for the n-type and/or p-type sub-regions arewithin the scope and spirit of this disclosure.

Gate structures 108 can include a gate dielectric layer 116 and a gateelectrode 118 disposed on gate dielectric layer 116. Gate structures 108can be formed by a gate replacement process.

In some embodiments, gate dielectric layer 116 can have a thickness 116t in a range from about 1 nm to about 5 nm. Gate dielectric layer 116can include silicon oxide and can be formed by CVD, atomic layerdeposition (ALD), physical vapor deposition (PVD), e-beam evaporation,or other suitable processes. In some embodiments, gate dielectric layer116 can include (i) a layer of silicon oxide, silicon nitride, and/orsilicon oxynitride, (ii) a high-k dielectric material, such as hafniumoxide (HfO₂), titanium oxide (TiO₂), hafnium zirconium oxide (HfZrO),tantalum oxide (Ta₂O₃), hafnium silicate (HfSiO₄), zirconium oxide(ZrO₂), zirconium silicate (ZrSiO₂), (iii) a high-k dielectric materialhaving oxides of lithium (Li), beryllium (Be), magnesium (Mg), calcium(Ca), strontium (Sr), scandium (Sc), yttrium (Y), zirconium (Zr),aluminum (Al), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium(Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb),dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium(Yb), or lutetium (Lu), or (iv) a combination thereof. High-k dielectriclayers can be formed by ALD and/or other suitable methods. In someembodiments, gate dielectric layer 116 can include a single layer or astack of insulating material layers. Other materials and formationmethods for gate dielectric layers 116 are within the scope and spiritof this disclosure.

In some embodiments, gate electrode 118 can include a gate barrier layer(not shown), a gate work function layer 122, and a gate metal fill layer124. Gate barrier layer can serve as a nucleation layer for subsequentformation of gate work function layer 122 and/or can help to preventsubstantial diffusion of metals (e.g., Al) from gate work function layer122 to underlying layers (e.g., gate dielectric layer 116). Gate barrierlayer can include titanium (Ti), tantalum (Ta), titanium nitride (TiN),tantalum nitride (TaN), or other suitable diffusion barrier materialsand can be formed by ALD, PVD, CVD, or other suitable metal depositionprocesses. In some embodiments, gate barrier layer can includesubstantially fluorine-free metal or metal-containing film and can beformed by ALD or CVD using one or more non-fluorine based precursors.The substantially fluorine-free metal or fluorine-free metal-containingfilm can include an amount of fluorine contaminants less than 5 atomicpercent in the form of ions, atoms, and/or molecules. In someembodiments, gate barrier layer can have a thickness ranging from about1 nm to about 10 nm. Other materials, formation methods and thicknessesfor gate barrier layer are within the scope and spirit of thisdisclosure.

Gate work function layer 122 can include a single metal layer or a stackof metal layers. The stack of metal layers can include metals havingwork function values equal to or different from each other. In someembodiments, gate work function layer 122 can include aluminum (Al),copper (Cu), tungsten (W), titanium (Ti), tantalum (Ta), titaniumnitride (TiN), tantalum nitride (TaN), nickel silicide (NiSi), cobaltsilicide (CoSi), silver (Ag), tantalum carbide (TaC), tantalum siliconnitride (TaSiN), tantalum carbon nitride (TaCN), titanium aluminum(TiAl), titanium aluminum nitride (TiAlN), tungsten nitride (WN), metalalloys, and/or combinations thereof. In some embodiments, gate workfunction layer 122 can include Al-doped metal, such as Al-doped Ti,Al-doped TiN, Al-doped Ta, or Al-doped TaN. Gate work function layer 122can be formed using a suitable process such as ALD, CVD, PVD, plating,or combinations thereof. In some embodiments, gate work function layer122 can have a thickness ranging from about 2 nm to about 15 nm. Othermaterials, formation methods and thicknesses for gate work functionlayer 122 are within the scope and spirit of this disclosure.

Gate metal fill layer 124 can include a single metal layer or a stack ofmetal layers. The stack of metal layers can include metals differentfrom each other. In some embodiments, gate metal fill layer 124 caninclude a suitable conductive material, such as Ti, silver (Ag), Al,titanium aluminum nitride (TiAlN), tantalum carbide (TaC), tantalumcarbo-nitride (TaCN), tantalum silicon nitride (TaSiN), manganese (Mn),Zr, titanium nitride (TiN), tantalum nitride (TaN), ruthenium (Ru),molybdenum (Mo), tungsten nitride (WN), copper (Cu), tungsten (W),cobalt (Co), nickel (Ni), titanium carbide (TiC), titanium aluminumcarbide (TiAlC), tantalum aluminum carbide (TaA1C), metal alloys, and/orcombinations thereof. Gate metal fill layer 124 can be formed by ALD,PVD, CVD, or other suitable deposition processes. Other materials andformation methods for gate metal fill layer 124 are within the scope andspirit of this disclosure.

Each of spacers 110 can include spacer portions 110 a that formsidewalls of gate structures 108 and are in contact with dielectriclayer 116, spacer portions 110 b that form sidewalls of fin structures104, and spacer portions 110 c that form protective layers on STIregions 112. Spacers 110 can include insulating material, such assilicon oxide, silicon nitride, a low-k material, or a combinationthereof. Spacers 110 can have a low-k material with a dielectricconstant less than 3.9 (e.g., less than 3.5, 3, or 2.8). In someembodiments, each of spacers 110 can have a thickness 110 t in a rangefrom about 5 nm to about 10 nm. Based on the disclosure herein, a personof ordinary skill in the art will recognize that other materials andthicknesses for spacers 110 are within the scope and spirit of thisdisclosure.

STI regions 112 can provide electrical isolation to semiconductor device100 from neighboring active and passive elements (not shown) integratedwith or deposited onto substrate 102. STI regions 112 can have adielectric material, such as silicon oxide, silicon nitride, siliconoxynitride, fluorine-doped silicate glass (FSG), a low-k dielectricmaterial, and/or other suitable insulating materials. In someembodiments, STI regions 112 can include a multi-layered structure.

Semiconductor device 100 can include additional elements, such as etchstop layers (ESLs) 228 and 240, interlayer dielectric (ILD) layers 230,232, and 244, S/D contact structures 235A, gate contact structures 235B,high resistance (high R) structure 242, dual metal capped via contactstructures 247A-247C, and interconnect structures 257A-257C, which areillustrated and described with reference to FIG. 2. FIG. 2 is across-sectional view of area 114 of semiconductor device 100 in FIG. 1.The area 114 can be along an XZ plane through epitaxial fin region 105and fin region 106 and gate structures 108 adjacent to them. Theseadditional elements of semiconductor device 100 are not shown in FIG. 1for the sake of clarity. Though FIG. 2 shows contact structure235A-235B, via contact structures 247A-247B, and interconnect structures257A-257B formed on one of fin structures 104 and gate structures 108,respectively, these structures can be similarly formed on the other finstructures 104 and gate structures 108 shown in FIG. 1.

Referring to FIG. 2, ESL 228 can be configured to protect gatestructures 108 and epitaxial fin regions 105 during subsequentprocessing. This protection can be provided, for example, during theformation of ILD layer 232, S/D contact structures 235A, and/or gatecontact structures 235B. ESL 228 can be disposed on sides of spacers 110and on epitaxial fin regions 105. In some embodiments, ESL 228 caninclude, for example, silicon nitride (SiN_(x)), silicon oxide(SiO_(x)), silicon oxynitride (SiON), silicon carbide (SiC), siliconcarbo-nitride (SiCN), boron nitride (BN), silicon boron nitride (SiBN),silicon carbon boron nitride (SiCBN), silicon nitride (SiN), siliconoxycarbide (SiOC), silicon oxycarbonitride (SiOCN), or a combinationthereof. In some embodiments, ESL 228 can include silicon nitride orsilicon oxide formed by low pressure chemical vapor deposition (LPCVD),plasma enhanced chemical vapor deposition (PECVD), chemical vapordeposition (CVD), or silicon oxide formed by a high-aspect-ratio process(HARP). In some embodiments, ESL 228 can have a thickness along a Z-axisin a range from about 1 nm to about 10 nm.

ESL 240 can be similar in material composition to ESL 228, according tosome embodiments. In some embodiments, ESL 240 can have a thicknessalong a Z-axis different from thickness of ESL 228 in a range from about5 nm to about 10 nm. ESL 240 can be disposed on ILD layer 232, S/Dcontact structures 235A, and gate contact structures 235B. Othermaterials, formation methods, and thicknesses for ESLs 228 and 240 arewithin the scope and spirit of this disclosure.

ILD layer 230 can be disposed on STI regions 112 and ESL 228 and caninclude a dielectric material deposited using a deposition methodsuitable for flowable dielectric materials (e.g., flowable siliconoxide, flowable silicon nitride, flowable silicon oxynitride, flowablesilicon carbide, or flowable silicon oxycarbide). For example, flowablesilicon oxide can be deposited using flowable CVD (FCVD). In someembodiments, the dielectric material can be silicon oxide. In someembodiments, ILD layer 230 can include silicon oxide (SiO₂), SiOC,zirconium oxide (ZrO₂), hafnium oxide (HfO₂), or dielectric materialswith high-k, low-k (e.g., k-value in a range from about 3.9 to about3.0), or extreme low-k (e.g., k-value in a range from about 2.9 to about2.0). In some embodiments, ILD layer 230 can have a thickness along aZ-axis in a range from about 50 nm to about 200 nm. In some embodiments,ILD layer 230 can include a stack of dielectric layers, where eachdielectric layer can have thickness along a Z-axis in a range from about1 nm to about 10 nm.

ILD layer 232 can be disposed on ILD layer 230 and can have a thicknessalong a Z-axis in a range from about 100 nm to about 600 nm. ILD layer244 can be disposed on ESL 240 and can have a thickness along a Z-axisin a range from about 100 nm to about 600 nm. In some embodiments, ILDlayers 232 and 244 can be similar in material composition to ILD layer230. In some embodiments, ILD layer 232 can include a dielectricmaterial, such as silicon oxycarbide, TEOS oxide, or a combinationthereof. In some embodiments, ILD layer 244 can include a low-kdielectric material having a k value less than about 3.0 (e.g., about2.8 or about 2.5). Other materials, thicknesses, and formation methodsfor ILD layers 230, 232, and 244 are within the scope and spirit of thisdisclosure.

Still referring to FIG. 2, S/D contact structures 235A can be configuredto electrically connect epitaxial fin regions 105 to other elements ofsemiconductor device 100 and/or of the integrated circuit (not shown).S/D contact structures 235A can be disposed on and in electrical contactwith epitaxial fin regions 105. In some embodiments, each of S/D contactstructures 235A can include (i) a silicide layer 236, (ii) a S/D contactbarrier layer 234A, and (iii) a S/D contact plug 238A.

Silicide layers 236 can be disposed on or within epitaxial fin regions105 and can have a thickness along a Z-axis in a range from about 4 nmto about 6 nm. Silicide layers 236 can provide a low resistanceinterface between epitaxial fin regions 105 and S/D contact plugs 238A.Silicide layers 236 can include Co, Ni, Ti, W, Mo, Ti, nickel cobaltalloy (NiCo), Pt, nickel platinum alloy (NiPt), Ir, platinum iridiumalloy (PtIr), Er, Yb, Pd, Rh, niobium (Nb), titanium silicon nitride(TiSiN), other refractory metals, or a combination thereof In someembodiments, silicide layers 236 can include a metal silicide-dopantcomplex material that can be formed from dopants included during theformation of silicide layers 236. Silicide layers 236 can have a dopantconcentration greater than 10²¹ atoms/cm³, 10²² atoms/cm³, or 10²³atoms/cm³. For n-type epitaxial fin regions 105, dopants in silicidelayers 236 can include phosphorus, arsenic, other n-type dopants, or acombination thereof. For p-type epitaxial fin regions 105, dopants insilicide layers 236 can include indium (In), gallium (Ga), other p-typedopants, or a combination thereof.

S/D contact barrier layers 234A can be disposed between silicide layers236 and S/D contact plugs 238A and along sidewalls of S/D contact plugs238A as shown in FIG. 2. S/D contact barrier layers 234A can beconfigured as diffusion barriers to prevent oxidation of silicide layers236 and diffusion of other unwanted atoms and/or ions into silicidelayers 236 during formation of S/D contact plugs 238A. In someembodiments, S/D contact barrier layers 234A can include a single layeror a stack of conductive materials such as, for example, TiN, Ti, Ni,TiSiN, TaN, Ta, or a combination thereof. In some embodiments, S/Dcontact barrier layers 234A can act as an adhesion-promoting-layer, aglue-layer, a primer-layer, a protective-layer, and/or anucleation-layer, for example, S/D contact barrier layers 234A can beTiN to improve Co adhesion. S/D contact barrier layers 234A can have athickness in a range from about 1 nm to about 3 nm, according to someembodiments.

S/D contact plugs 238A can be disposed within ILD layers 230 and 232 andon silicide layers 236 and can include a conductive material, such asRu, Ir, Ni, Os, Rh, Al, Mo, W, Co, or Cu. In some embodiments, S/Dcontact plugs 238A can include a conductive material with lowresistivity (e.g., about 50 μΩ-cm, about 30 μΩ-cm, or about 10 μΩ-cm).The portions of S/D contact plugs 238A in ILD layers 230 and 232 canhave material composition and/or resistivity similar to or differentfrom each other. In some embodiments, S/D contact plugs 238A can includea stack of three layers, for example, a first layer of Co deposited byPVD, a second layer of Co deposited by CVD, and a third layer of Codeposited by ECP followed by a thermal reflow to form void-free Co-basedS/D contact plugs 238A.

In some embodiments, S/D contact plugs 238A can include horizontaldimensions (e.g., width or diameter) along an X-axis in a range fromabout 10 nm to about 15 nm or less than about 20 nm. S/D contact plugs238A can have vertical dimensions (e.g., thickness) along a Z-axisranging from about 50 nm to about 150 nm. S/D contact plugs 238A canhave a high aspect ratio ranging from about 5 to about 15, where theaspect ratio can be a ratio of their vertical dimensions (e.g., height)along a Z-axis to their horizontal dimensions (e.g., width or diameter)along an X-axis. In some embodiments, the aspect ratio ranges from about5 to about 8.

Referring to FIG. 2, gate contact structures 235B can be configured toelectrically connect gate structures 108 to other elements ofsemiconductor device 100 and/or of the integrated circuit. Gate contactstructures 235B can be disposed within ILD layer 232 and on gatestructures 108. Each of gate contact structures 235B can include (i) agate contact barrier layer 234B and (ii) a gate contact plug 238B. Theabove discussion of the material composition of S/D contact barrierlayers 234A and S/D contact plugs 238A applies to gate contact barrierlayers 234B and gate contact plugs 238B, respectively, unless mentionedotherwise.

High R structure 242 can be a resistor in semiconductor device 100and/or of the IC. High R structure 242 can be disposed on ESL 240 orwithin multiple layers of ESL 240. High R structure 242 can include TiNor TaN and can have a vertical dimension along a Z-axis (e.g.,thickness) from about 4 nm to about 6 nm.

Via contact structures 247A-247B can be disposed within ESL 240 and ILDlayers 232 and 244, and on respective S/D contact plugs 238A and gatecontact plugs 238B. Via contact structures 247C can be disposed withinESL 240 and on high R structure 242. In some embodiments, via contactstructures 247A-247C include horizontal dimensions (e.g., width ordiameter) along an X-axis in a range from about 10 nm to about 15 nm. Insome embodiments, via contact structures 247A-247C has an aspect ratioin a range from about 3 to about 15. In some embodiments, via contactstructures 247A-247C has an aspect ratio in a range from about 5 toabout 8. Via contact structures 247A-247C can include (i) bottom metalcapping layer 246A-246C, (ii) via contact plugs 248A-248C disposed onbottom metal capping layer 246A-246C, and (iii) top metal capping layer250A-250C disposed on via contact plugs 248A-248C.

Bottom metal capping layers 246A-246C can be disposed on S/D contactplugs 238A, gate contact plugs 238B, and high R structure 242,respectively. Bottom metal capping layers 246A-246C can include aconductive material, such as tungsten (W) and can be formed by aselective bottom-up metal deposition process (e.g., bottom-up CVDprocess), or other suitable processes. In some embodiments, bottom metalcapping layers 246A-246C can be deposited at a temperature from about250° C. to about 300° C. under a pressure from about 5 Torr to about 15Torr using reaction gases, such as tungsten hexafluoride (WF₆) as aW-based precursor and H₂. The materials (e.g., W) of bottom metalcapping layers 246A-246C can have a higher deposition selectivity forthe bottom surfaces of contact openings 962A-962C (not shown in FIG. 2;shown in FIG. 9) of respective via contact structures 247A-247C than thesidewalls of contact openings 962A-962C, thus forming void-free bottommetal capping layers 246A-246C. In some embodiments, bottom metalcapping layer 246A-246C can have vertical dimensions 246 t (e.g.,thickness) along a Z-axis ranging from about 2 nm to about 4 nm. In someembodiments, bottom metal capping layers 246A-246C can preventcorrosions of S/D contact plugs 238A and gate contact plugs 238B duringsubsequent processes. In some embodiments, the resistance of via contactstructures 247A-247C can be large if 246 t is larger than 4 nm. In someembodiments, bottom metal capping layer 246A-246C cannot preventcorrosion of S/D contact plugs 238A and gate contact plugs 238B if 246 tis smaller than 2 nm.

Via contact plugs 248A-248C can be disposed on respective bottom metalcapping layers 246A-246C. Via contact plugs 248A-248C can include Ru,Ir, Ni, Os, Rh, Al, Mo, W, Co, Cu and/or other suitable low-resistivitymaterials. In some embodiments, via contact plugs 248A-248C can beformed by a selective bottom-up metal deposition process (e.g.,bottom-up CVD process) at a temperature ranging from about 150° C. toabout 300° C. under a pressure ranging from about 5 Torr to about 15Torr using reaction gases, such as Ru-based precursor and H₂. Thematerials (e.g., Ru) of via contact plugs 248A-248C can have a higherdeposition selectivity for the top surfaces of bottom metal cappinglayers 246A-246C than the sidewalls of the contact openings 962A-962C,thus forming void-free via contact plugs 248A-248C.

Via contact plugs 248A-248C can have larger horizontal dimensions at thetop than at the bottom. In some embodiments, via contact plugs 248A-248Chave horizontal dimensions (e.g., width or diameter) 248 d 1 along anX-axis at the top of via contact plugs 248A-248C ranging from about 10nm to about 15 nm. In some embodiments, via contact plugs 248A-248C havehorizontal dimensions (e.g., width or diameter) 248 d 2 along an X-axisat the bottom of via contact plugs 248A-248C ranging from about 10 nm toabout 12 nm. In some embodiments, via contact plugs 248A-248C havevertical dimensions (e.g., thickness) 248 t along a Z-axis ranging fromabout 30 nm to about 150 nm. In some embodiments, via contact plugs248A-248C have an aspect ratio ranging from about 5 to about 8, wherethe aspect ratio can be a ratio of their vertical dimensions (e.g.,height) along a Z-axis to their top horizontal dimensions (e.g., widthor diameter 248 d 1) along an X-axis. In some embodiments, a thicknessratio of 248 t to 246 t ranges from about 7 to about 80. In someembodiments, Ru-based via contact plugs 248A-248C with dimensions fromabout 10 nm to about 15 nm and with aspect ratio from about 5 to about 8have lower resistivity compared to W- or Co-based via contact plugs248A-248C with similar dimensions. In some embodiments, a criticaldimension 248 w between the top of via contact plugs 248A-248B rangesfrom about 5 nm to about 8 nm to prevent electrical short between S/Dcontact structures 235A and gate contact structures 235B.

Top metal capping layers 250A-250C can be disposed on via contact plugs248A-248C. The above discussion of bottom metal capping layers 246A-246Capplies to top metal capping layer 250A-250C, unless mentionedotherwise. Top metal capping layers 250A-250C can have verticaldimensions 250 t (e.g., thickness) along a Z-axis ranging from about 2nm to about 4 nm. In some embodiments, a thickness ratio of 248 t to 250t ranges from about 7 to about 80. In some embodiments, top metalcapping layers 250A-250C can prevent electromigration of metals (e.g.,Cu) from overlying respective interconnect structures 257A-257C. In someembodiments, the resistance of via contact structures 247A-247C can belarge if 250 t is larger than 4 nm. In some embodiments, top metalcapping layer 250A-250C cannot prevent electromigration of metals (e.g.,Cu) from overlying respective interconnect structures 257A-257C if 250 tis smaller than 2 nm.

According to some embodiments, via contact structures 247A-247C withW-based bottom metal capping layers 246A-246C, Ru-based via contactplugs 248A-248C, and W-based top metal capping layers 250A-250C havingdimensions from about 10 nm to about 15 nm and aspect ratio from about 5to about 8 can have lower resistivity compared to W- or Co-based viacontact structures 247A-247C with similar dimensions. In someembodiments, dual metal capped via contact structures 247A-247C canreduce contact resistivity by about 10% to about 30% compared to viacontact structures without dual metal capping layers. Dual metal cappedvia contact structures 247A-247C can also prevent corrosions of S/Dcontact plugs 238A and gate contact plugs 238B and preventelectromigration of metals from overlying interconnect structures257A-257C.

Interconnect structures 257A-257C can be disposed on respective viacontact structures 247A-247C. In some embodiments, interconnectstructures 257A-257C can include barrier layers 256 and conductive lines258. In some embodiments, barrier layers 256 can include a single layeror a stack of conductive materials including such as, TiN, Ti, Ni, TaN,Ta, Co, or a combination thereof. In some embodiments, barrier layers256 can act as an adhesion-promoting-layer, a glue-layer, aprimer-layer, a protective-layer, and/or a nucleation-layer. Barrierlayers 256 can have a thickness in a range from about 1 nm to about 5nm. In some embodiments, barrier layers 256 can include a first TaNlayer deposited by ALD with a thickness ranging from about 0.5 nm toabout 1.5 nm, a second TaN layer, on the first TaN layer, deposited byPVD with a thickness ranging from about 0.5 nm to about 1.5 nm, a Coliner, on the second TaN layer, deposited by CVD with a thicknessranging from about 1 nm to about 3 nm, and a Cu seed layer, on the Coliner, deposited by PVD with a thickness ranging from about 1 nm toabout 2 nm.

Conductive lines 258 can include conductive material such as, W, Al, Co,or Cu and can be deposited using CVD or other suitable metal depositionprocess. In some embodiments, conductive lines 258 can include a singlelayer or a stack of conductive materials. In some embodiments,conductive lines 258 can have horizontal dimension (e.g., width) alongan X-axis ranging from about 20 nm to about 25 nm. In some embodiment,conductive lines 258 can have an aspect ratio ranging from about 2 toabout 3, where the aspect ratio can be a ratio of their verticaldimensions (e.g., height) along a Z-axis to their horizontal dimensions(e.g., width) along an X-axis.

Semiconductor device 100 can further include an ESL 252 disposed on ILDlayer 244 and a low-k layer 254 disposed on ESL 252. Interconnectstructures 257A-257C can be formed within ESL 252 and low-k layer 254 asshown in FIG. 2. In some embodiments, ESL 252 can include aluminum oxide(AlO_(x)) deposited by ALD. In some embodiments, ESL 252 can bedeposited using trimethylaluminum (TMA) and H₂O as precursors at atemperature ranging from about 200° C. to about 350° C. In someembodiments, ESL 252 can have a vertical dimension (e.g., thickness)along a Z-axis ranging from about 3 nm to about 5 nm. In someembodiments, low-k layer 254 can include low-k materials having adielectric constant less than about 3.9. In some embodiments, low-kmaterial can include SiOC, SiCN, SiOCN, SiOCH, porous SiO₂, and/or acombination thereof. In some embodiments, low-k layer 254 can have avertical dimension (e.g., thickness) along a Z-axis ranging from about50 nm to about 60 nm. In some embodiments, low-k layer 254 can reducetime delay of semiconductor device 100.

FIG. 3 is a flow diagram of an example method 300 for fabricatingsemiconductor device 100, according to some embodiments. Forillustrative purposes, the operations illustrated in FIG. 3 will bedescribed with reference to the example fabrication process forfabricating semiconductor device 100 as illustrated in FIGS. 4-13. FIGS.4-13 are cross-sectional views of area 114 of semiconductor device 100in FIG. 1 at various stages of its fabrication process, according tosome embodiments. Operations can be performed in a different order ornot performed depending on specific applications. It should be notedthat method 300 may not produce a complete semiconductor device 100.Accordingly, it is understood that additional processes can be providedbefore, during, and after method 300, and that some other processes mayonly be briefly described herein. Elements in FIGS. 4-13 with the sameannotations as elements in FIGS. 1-2 are described above.

In operation 310, contact structures are formed on epitaxial fin regionsand gate structures. For example, as described with reference to FIGS.4-6, S/D contact structures 235A (shown in FIG. 6) can be formed onepitaxial fin regions 105 and gate contact structures 235B (shown inFIG. 6) can be formed on gate structures 108. The formation of S/Dcontact structures 235A and gate contact structures 235B can includesequential steps of: (i) forming S/D contact openings 460A and gatecontact openings 460B (shown in FIG. 4); (ii) selectively formingsilicide layers 236 within S/D contact openings 460A and on epitaxialfin regions 105 (shown in FIG. 5); and (iii) forming contact barrierlayers 234A-234B and contact plugs 238A-238B (shown in FIG. 6).

Referring to FIG. 4, the formation of contact openings 460A-460B caninclude blanket depositing ILD layer 232 on ILD layer 230, epitaxial finregions 105, and gate structures 108. ILD layer 232 can include adielectric material deposited using a deposition method suitable forflowable dielectric materials (e.g., flowable silicon oxide, flowablesilicon nitride, flowable silicon oxynitride, flowable silicon carbide,or flowable silicon oxycarbide). For example, flowable silicon oxide canbe deposited using flowable CVD (FCVD). In some embodiments, thedielectric material can be silicon oxide, silicon oxycarbide, TEOSoxide, or a combination thereof. In some embodiments, ILD layer 232 caninclude silicon oxide (SiO₂), SiOC, zirconium oxide (ZrO₂), hafniumoxide (HfO₂), or dielectric materials with high-k, low-k (e.g., k-valuein a range from about 3.9 to about 3.0), or extreme low-k (e.g., k-valuein a range from about 2.9 to about 2.0). In some embodiments, ILD layer232 can have a thickness along a Z-axis in a range from about 100 nm toabout 600 nm.

The formation of ILD layer 232 can be followed by an etching of ILDlayer 232 to form contact openings 460A-460B on epitaxial fin regions105 and gate structures 108, respectively. Prior to the etching of ILDlayer 232, a patterned photoresist layer and a hard mask layer can beformed on ILD layer 232. Portions of the hard mask layer not covered bythe patterned photoresist layer can be etched to expose underlying ILDlayer 232. The exposed ILD layer 232 can be etched to form contactopenings 460A-460B followed by the removal of the patterned photoresistlayer and the hard mask layer. Contact openings 460A-460B can be formedby a dry etching process. In some embodiments, the dry etching processcan include fluorine or chlorine based etchants followed by a wet cleanprocess. In some embodiments, the wet clean process can include using asolution of de-ionized water (DI), NH₄OH, and H₂O₂.

Referring to FIG. 5, the selective formation of silicide layers 236 caninclude sequential steps of: (i) a pre-deposition cleaning, (ii) blanketdepositing a contact barrier layer 234*, (iii) thermal annealing theblanket deposited contact barrier layer 234*, and (iv) removingthermally annealed contact barrier layer 234*. The pre-depositioncleaning can be performed on the structure of FIG. 4 and can include adirectional dry etch process to clean the bottom surfaces of contactopenings 460A-460B and an isotropic dry etch process (e.g., SiCoNi etchprocess), which includes using a remote plasma assisted dry etch processthat involves the simultaneous exposure of contact openings 460A-460B toH₂, NF₃, and NH₃ plasma by-products to clean the bottom surfaces andsidewalls of contact openings 460A-460B. The directional dry etchprocess can include using fluorine based etchants, such as nitrogentrifluoride (NF₃) and ammonia (NH₃). The directional dry etch processcan be performed at a temperature ranging from about 50° C. to about120° C. The isotropic dry etch process can also include using fluorinebased etchants (e.g., NF₃ and NH₃), but without any bias. The isotropicdry etch process can be performed at a temperature ranging from about150° C. to about 210° C.

Contact barrier layer 234* can be blanket deposited on the structure ofFIG. 4 after the pre-deposition cleaning process. Contact barrier layer234* can be substantially conformally deposited within contact openings460A-460B and on the top surface of ILD layer 232 by PVD, ALD, and/orother suitable deposition methods. In some embodiments, contact barrierlayer 234* can include a single layer or a stack of conductive materialssuch as, TiN, Ti, Ni, TiSiN, TaN, Ta, or a combination thereof. Contactbarrier layer 234* can have a thickness in a range from about 1 nm toabout 3 nm, according to some embodiments. In some embodiments, contactbarrier layers 234* can include a stack of two layers, for example, alayer of Ti deposited by PVD with a thickness ranging from about 5 nm toabout 15 nm and a layer of TiN deposited by ALD with a thickness rangingfrom about 1 nm to about 5 nm.

The thermal annealing process can be performed on the structure of FIG.4 after the blanket deposition of contact barrier layer 234* at atemperature ranging from about 450° C. to about 700° C. In someembodiments, the thermal annealing process can be performed in nitrogenat an atmospheric pressure for a period ranging from about 10 seconds toabout 20 seconds. After the thermal annealing process, silicide layers236 can be selectively formed between epitaxial fin regions 105 andcontact barrier layers 234* due to a silicidation reaction between theSi-based material of epitaxial fin regions 105 and contact barrier layer234*. There is no silicide layers formed between gate structures 108 andcontact barrier layer 234* because of the absence of silicon-basedmaterial in metal gate structures 108, unlike epitaxial fin regions 105.Silicide layers 236 can have vertical dimensions (e.g., thickness) alonga Z-axis in a range from about 4 nm to about 6 nm. Silicide layers 236can provide a low resistance interface between epitaxial fin regions 105and subsequently formed S/D contact plugs 238A.

The removal of contact barrier layer 234* from the structure of FIG. 5can include a wet etch process. The wet etch process can include using asolution of de-ionized water (DI), NH₄OH, and H₂O₂ or other suitableetchants. In some embodiments, contact barrier layer 234* can beoxidized and removed while silicide layers 236 can remain on epitaxialfin regions 105.

The removal of contact barrier layers 234* can be followed by theformation of contact barrier layers 234A-234B and contact plugs238A-238B, which can include sequential steps of: (i) Ar-based cleaning,(ii) blanket depositing the material(s) for contact barrier layers234A-234B, (iii) blanket depositing the material(s) for contact plugs238A-238B, and (iv) chemical mechanical polishing (CMP) the blanketdeposited material(s) for contact barrier layers 234A-234B and contactplugs 238A-238B.

The Ar-based cleaning can be performed to remove surface oxides from thetop surfaces of gate structures 108 and silicide layers 236. In someembodiments, the Ar-based cleaning can be performed using Ar gas at aflow rate ranging from about 5 sccm to about 20 sccm with a source RFpower ranging from about 250 W to about 350 W and a bias RF powerranging from about 400 W to about 500 W for a period ranging from about2 seconds to about 8 seconds. The material(s) for contact barrier layers234A-234B can be blanket deposited on the structure of FIG. 5 after theremoval of contact barrier layer 234* and the Ar-based cleaning. Theabove discussion of the deposition process and materials of contactbarrier layers 234* applies to the deposition process and materials ofcontact barrier layers 234A-234B, unless mentioned otherwise. In someembodiments, contact barrier layers 234A-234B can include TiN depositedby ALD with a thickness ranging from about 1 nm to about 2 nm.

The material(s) for contact plugs 238A-238B can be blanket deposited onthe blanket deposited material(s) for contact barrier layers 234A-234B.In some embodiments, contact plugs 238A-238B can include a stack ofthree metal layers, for example, a layer of first metal (e.g., Ru, Ir,Ni, Os, Rh, Al, Mo, W, or Co) deposited by PVD, a layer of second metal(e.g., Ru, Ir, Ni, Os, Rh, Al, Mo, W, or Co) deposited by CVD on thefirst metal, and a layer of third metal (e.g., Ru, Ir, Ni, Os, Rh, Al,Mo, W, or Co) deposited by electrochemical plating (ECP) on the secondmetal, where the first, second, and third metal can be similar to ordifferent from each other. The layer of first metal can be depositeddirectionally and selectively on the bottom surfaces of contact openings460A-460B and on the top surface of ILD layer 232 with a thicknessranging from about 5 nm to about 10 nm and not along the sidewalls ofcontact openings 460A-460B. The layer of second metal can be depositedconformally on the layer of first metal and along the sidewalls ofcontact openings 460A-460B with a thickness ranging from about 1 nm toabout 3 nm. The layer of third metal can fill the remaining portions ofcontact openings 460A-460B that are not filled by the layers of firstand second metal.

A thermal reflow process can follow the deposition of the material(s)for S/D contact plugs 238A and gate contact plugs 238B to form void-freecontact structures 235A-235B. For example, a thermal reflow process canreflow the first, second, third metals and form void-free contactstructures 235A-235B for three layers of metal (e.g., Ru, Ir, Ni, Os,Rh, Al, Mo, W, or Co) deposited by PVD, CVD, and ECP. The thermal reflowprocess can be performed in a gas mixture of hydrogen and nitrogen orinert gases (e.g., Ar). In some embodiments, the gas mixture can includehydrogen at a concentration higher than 30%. The thermal reflow processcan be performed at a temperature ranging from about 300° C. to about400° C. for a period ranging from about 1 min to about 10 min. Thethermal reflow can be followed by the CMP process to substantiallycoplanarize the top surfaces of S/D contact structures 235A, gatecontact structures 235B, and ILD layer 232, as shown in FIG. 6.

Referring back to FIG. 3, in operation 320, high resistance structuresare formed adjacent to the gate contact structures and the S/D contactstructures. For example, as described with reference to FIGS. 7-8, highresistance structure 242 can be formed adjacent to S/D contactstructures 235A and gate contact structures 235B. The process forforming high resistance structure 242 can include sequential steps of:(i) blanket depositing a first ESL 740A (shown in FIG. 7); (ii) blanketdepositing a layer of high resistive material on first ESL 740A; (iii)blanket depositing a second ESL 740B on the layer of high resistivematerial; (iv) etching a portion of second ESL 740B and the layer ofhigh resistive material (shown in FIG. 7); (v) blanket depositing athird ESL on the etched second ESL 740B and the layer of high resistivematerial; (vi) blanket depositing the material(s) for ILD layer 244 onthe third ESL; and (vii) chemical mechanical polishing (CMP) the blanketdeposited third ESL and the material(s) for ILD 244.

Referring to FIG. 7, first ESL 740A can be blanket deposited on thestructure of FIG. 6. The above discussion of ESL 240 applies to firstESL 740A, unless mentioned otherwise. In some embodiments, first ESL740A can be blanket deposited by ALD or CVD with a thickness along aZ-axis ranging from about 0.5 nm to about 2 nm. In some embodiments,first ESL 740A can include silicon nitride (SiN_(x)). In someembodiment, the blanket deposition of first ESL 740A can be performed ata temperature ranging from about 300° C. to about 500° C.

The layer of high resistive material can be blanket deposited on firstESL 740A. In some embodiments, the layer of high resistive material canbe blanket deposited by PVD with a thickness along a Z-axis ranging fromabout 1 nm to 7 nm. The above discussion of first ESL 740A applies tosecond ESL 740B, unless mentioned otherwise. Second ESL 740B can have athickness along a Z-axis ranging from about 0.5 nm to about 1.5 nm.Second ESL 740B and the layer of high resistive material can bepatterned and etched by a dry etch process. In some embodiments, the dryetch process can include chlorine-based etchants and followed by adiluted (e.g., 500:1) HF clean. A portion of second ESL 740B and thelayer of high resistive material can be removed after the etchingprocess, and high R structure 242 can be formed as shown in FIG. 7.

Referring to FIG. 8, the third ESL and the material (s) for ILD layer244 can be blanket deposited on the structure of FIG. 7. The abovediscussion of first ESL 740A applies to the third ESL, unless mentionedotherwise. In some embodiments, the third ESL can have a thickness alonga Z-axis ranging from about 0.5 nm to about 1.5 nm. In some embodiments,the material (s) for ILD layer 244 can be blanket deposited on the thirdESL by CVD with a thickness along a Z-axis ranging from about 10 nm toabout 30 nm. The blanket deposition of the third ESL and the material(s) for ILD layer 244 can be followed by a CMP process to form ESL 240and ILD layer 244 as shown in FIG. 8, and substantially coplanarize thetop surfaces of ESL 240 and ILD layer 244.

Referring back to FIG. 3, in operation 330, bottom metal capping layersare formed on the S/D contact structures, gate contact structures, andhigh R structures. For example, as described with reference to FIGS.9-11, bottom metal capping layers 246A-246C can be formed on S/D contactstructures 235A, gate contact structures 235B, and high R structure 242,respectively, (shown in FIG. 11). The process for forming bottom metalcapping layers 246A-246C can include sequential steps of: (i) formingvia contact openings 962A-962C (shown in FIG. 9); (ii) forming contactplug recesses 1062A-1062B in S/D contact plugs 238A and gate contactplugs 238B (shown in FIG. 10); and (iii) in-situ selectively bottom-updepositing the material(s) for bottom metal capping layers 246A-246Cwithin contact plug recesses 1062A-1062B and via contact opening 962C(shown in FIG. 11).

Referring to FIG. 9, via contact openings 962A-962C can be formed on S/Dcontact structures 235A, gate contact structures 235B, and high Rstructure 242, respectively. A patterned photoresist layer can be formedon the structure of FIG. 8. Portions of ILD layer 244 and ESL 240 notcovered by the patterned photoresist layer can be etched to form viacontact openings 962A-962C. Etching of ILD layer 244 and ESL 240 caninclude a dry etch process. In some embodiments, the dry etching processcan include fluorine or chlorine based etchants followed by a wet cleanprocess. Other etching methods and processes for via contact opening arewithin the scope and spirit of this disclosure.

In some embodiments, via contact openings 962A-962C can have horizontaldimensions (e.g., width or diameter) 248 d 1* along an X-axis at the topof via contact openings 962 ranging from about 10 nm to about 15 nm. Insome embodiments, via contact openings 962A-962C can have horizontaldimensions (e.g., width or diameter) 248 d 2* along an X-axis at thebottom of via contact openings 962A-962C ranging from about 10 nm toabout 12 nm. In some embodiments, via contact openings 962A-962C canhave vertical dimensions (e.g., thickness) 248 t* along a Z-axis rangingfrom about 30 nm to about 150 nm. In some embodiments, via contactopenings 962A-962C can have an aspect ratio ranging from about 5 toabout 8, where the aspect ratio can be a ratio of their verticaldimensions (e.g., height) along a Z-axis to their top horizontaldimensions (e.g., width or diameter 248 d 1*) along an X-axis.

Referring to FIG. 10, contact plug recesses 1062A-1062B in S/D contactplugs 238A and gate contact plugs 238B can be formed by etching backcontact plugs 238A-238B, respectively. The etch back process can includea wet etch process performed on the structure of FIG. 9. In someembodiment, the wet etch process can selectively etch S/D contact plugs238A and gate contact plugs 238B without etching high R structure 242.In some embodiments, the wet etch process can include using a solutionof de-ionized water (DI), NH₄OH, and H₂O₂ at a temperature ranging fromabout 20° C. to about 50° C. for a period ranging from about 3 secondsto about 120 seconds. After the etch back process, S/D contact plugs238A and gate contact plugs 238B can be recessed by a vertical dimension246 t* (e.g., thickness) along a Z-axis ranging from about 2 nm to about4 nm to form contact plug recesses 1062A-1062B. Other etching methods,etchants, etching temperatures, times, and recess dimensions for contactplug recesses 1062A-1062B are within the scope and spirit of thisdisclosure.

Referring to FIG. 11, bottom metal capping layers 246A-246C can beformed on recessed S/D contact plugs 238A, recessed gate contact plugs238B, and high R structure 242, respectively. Prior to the formation ofbottom metal capping layers 246A-246C, a thermal annealing in H₂ can beperformed to remove surface oxides from top surfaces of recessed S/Dcontact plugs 238A, gate contact plugs 238B, and high R structure 242 toform substantially oxide-free (e.g., no oxide) top surfaces of recessedS/D contact plugs 238A, gate contact plugs 238B, and high R structure242. The removal of these surface oxides can increase the depositionselectivity of the metal(s) of bottom metal capping layers 246A-246C toS/D contact plugs 238A, gate contact plugs 238B, and high R structure242 than to the sidewalls of via contact openings 962A-962C, thusallowing selective bottom-up deposition of the metal(s) of bottom metalcapping layers 246A-246C in subsequent formation of substantiallyvoid-free (e.g., no voids) bottom metal capping layers 246A-246C. Insome embodiments, the H₂ thermal annealing can be performed using a H₂gas mixture at a flow rate ranging from about 3000 sccm to about 6000sccm under a pressure ranging from about 5 Torr to about 30 Torr. Theconcentration of H₂ gas in the H₂ gas mixture can range from about 10%to about 50% and the H₂ thermal annealing can be performed at atemperature ranging from about 350° C. to about 450° C. such that thesurface oxides can be removed after the H₂ thermal annealing. Othermethods to remove surface oxides are within the scope and spirit of thisdisclosure.

The H₂ thermal annealing can be followed by the in-situ selectivebottom-up deposition of the metal(s) of bottom metal capping layers246A-246C. In some embodiments, the in-situ selective bottom-updeposition can include a CVD process and can be performed at atemperature ranging from about 250° C. to about 300° C. under a pressurefrom about 5 Torr to about 15 Torr using reaction gases, such as WF₆ andH₂. In some embodiments, bottom metal capping layers 246A-246C can havevertical dimensions 246 t (e.g., thickness) along a Z-axis ranging fromabout 2 nm to about 4 nm based on the process time. In some embodiments,bottom metal capping layers 246A-246C can prevent corrosions of S/Dcontact plugs 238A and gate contact plugs 238B during subsequentprocesses. Other deposition methods, processes, and dimension of bottommetal capping layers 246A-246C are within the scope and spirit of thisdisclosure.

Referring back to FIG. 3, in operation 340, via contact plugs are formedon the bottom metal capping layers. For example, as described withreference to FIGS. 12-13, via contact plugs 248A-248C can be formed onrespective bottom metal capping layers 246A-246C. The process forforming via contact plugs 248A-248C can include sequential steps of: (i)Ar cleaning top surfaces of bottom metal capping layers 246A-246C; (ii)in-situ selectively bottom-up depositing the metal(s) for via contactplugs 248A-248C; (iii) chemical mechanical polishing (CMP) the depositedmetal(s) (shown in FIG. 12); and (iv) etching back the chemicalmechanical polished metal(s) (shown in FIG. 13).

The Ar cleaning process can include an Ar plasma etch and can beperformed on the structure of FIG. 11 to remove surface oxides from topsurfaces of bottom metal capping layers 246A-246C to form substantiallyoxide-free (e.g., no oxide) top surfaces of bottom metal capping layers246A-246C. The removal of these surface oxides can increase thedeposition selectivity of the metal(s) of via contact plugs 248A-248C tobottom metal capping layers 246A-246C than to the sidewalls of viacontact openings 962A-962C, thus allowing selective bottom-up depositionof the metal(s) of via contact plugs 248A-248C in subsequent formationof substantially void-free (e.g., no voids) via contact plugs 248A-248C.In some embodiments, the Ar cleaning process can be performed using Argas at a flow rate ranging from about 5 sccm to about 20 sccm for aperiod ranging from about 2 seconds to about 8 seconds. In someembodiments, the Ar cleaning process can be performed with source RFpower ranging from about 250 W to about 350 W and bias RF power rangingfrom about 400 W to about 500 W. Other cleaning process methods andprocesses are within the scope and spirit of this disclosure.

The Ar cleaning process can be followed by in-situ selective bottom-updeposition of the metal(s) for via contact plugs 248A-248C within viacontact openings 962A-962C. In some embodiments, the in-situ selectivebottom-up deposition process can include a CVD process and can beperformed at a temperature ranging from about 150° C. to about 300° C.under a pressure from about 5 Torr to about 15 Torr using reactiongases, such as Ru-based precursor and H₂. In some embodiments, theRu-based precursors can include Ruthenium,tricarbonyl[(1,2,4,5-.eta.)-1-methyl-1,4-cyclohexadiene] (C₁₀H₁₀O₃Ru),(η6-benzene)((η6-benzene)(η4-1,3-cyclohexadiene) ruthenium(Ru(C6H6)(C6H8)), Ruthenium(III) acetylacetonate 1,3-cyclohexadiene(Ru(C₅H₇O₂)₃), (tricarbonyl) ruthenium(0) (Ru(CO)₃(C₆H₈)),Bis(ethylcyclopentadienyl) Ruthenium(II) (Ru(C₅H₄C₂H₅)₂); Rutheniumpentacarbonyl (Ru(CO)₅), or Triruthenium dodecacarbonyl (Ru₃(CO)₁₂).

The CMP process following the selective bottom-up deposition process canbe an ex-situ CMP process to substantially coplanarize top surfaces ofthe metal(s) deposited within via contact openings to form via contactplugs 248A*-248C* as shown in FIG. 12. Subsequently, via contact plugs248A*-248C* can be etched back to form via contact plugs 248A-248C asshown in FIG. 13. In some embodiments, the etch back process can includea wet etch process that can include using a solution of de-ionized water(DI), NH₄OH, and H₂O₂ at a temperature ranging from about 20° C. toabout 50° C. for a period ranging from about 3 seconds to about 120seconds. In some embodiments, the wet etch process can etch back viacontact plugs 248A-248C by a vertical dimension (e.g., thickness) alonga Z-axis ranging from about 2 nm to about 4 nm.

Referring back to FIG. 3, in operation 350, top metal capping layers areformed on the via contact plugs. For example, as described withreference to FIG. 13, top metal capping layers 250A-250C can be formedon via contact plugs 248A-248C. The process for forming top metalcapping layers 250A-250C can include sequential steps of: (i) thermalannealing via contact plugs 248A-248C in H₂; (ii) in-situ selectivelybottom-up depositing the metal(s) for top metal capping layer 250A-250C;and (iii) chemical mechanical polishing (CMP) the deposited metal(s)(shown in FIG. 12).

The above discussion of H₂ thermal annealing prior to the formation ofbottom metal capping layers 246A-246C and the in-situ selectivebottom-up deposition of the metal(s) of bottom metal capping layers246A-246C applies to top metal capping layer 250A-250C, unless mentionedotherwise. The H₂ thermal annealing process can remove surface oxidesfrom top surfaces of via contact plugs 248A-248C to form substantiallyoxide-free (e.g., no oxide) top surfaces of via contact plugs 248A-248Cselective bottom-up deposition of the metal(s) of top metal cappinglayer 250A-250C for subsequent formation of substantially void-free(e.g., no voids) top metal capping layers 250A-250C. The CMP process cansubstantially coplanarize top surfaces of the metal(s) deposited withtop surfaces of ESL 240 and ILD 244 as shown in FIG. 13. Top metalcapping layer 250A-250C can have vertical dimensions 250 t (e.g.,thickness) along a Z-axis ranging from about 2 nm to about 4 nm.

Referring back to FIG. 3, in operation 360, interconnect structures areformed on the top metal capping layers. For example, as described withreference to FIGS. 2 and 13, interconnect structures 257A-257C can beformed on the structure of FIG. 13. Interconnect structures 257A-257Ccan include barrier layers 256 and conductive lines 258. The process forforming interconnect structures 257A-257C can include sequential stepsof: (i) blanket depositing ESL 252; (ii) blanket depositing low-k layer254 on ESL 252; (iii) forming interconnect openings (not shown); (iv)blanket depositing the material(s) for barrier layers 256; (v) blanketdepositing the material(s) for conductive lines 258; and (vi) chemicalmechanical polishing (CMP) the blanket deposited material(s) to form thestructure of FIG. 2.

In some embodiments, ESL 252 can include aluminum oxide (AlO_(x))deposited by ALD. In some embodiments, ESL 252 can be deposited by ALDusing trimethylaluminum (TMA) and H₂O as precursors at a temperatureranging from about 200° C. to about 350° C. In some embodiments, ESL 252can have a vertical dimension (e.g., thickness) along a Z-axis rangingfrom about 3 nm to about 5 nm.

Low-k layer 254 can include low-k materials having a dielectric constantless than about 3.9) deposited by ALD. In some embodiments, low-kmaterial can include SiOC, SiCN, SiOCN, SiOCH, porous SiO₂, and/or acombination thereof. In some embodiments, low-k layer 254 can have avertical dimension (e.g., thickness) along a Z-axis ranging from about50 nm to about 60 nm.

Interconnect openings can include etching of ESL 252 and low-k layer254. A patterned photoresist layer and a hard mask layer can be formedon low-k layer 254. Portions of the hard mask layer not covered by thepatterned photoresist layer can be etched to expose underlying low-klayer 254. The exposed low-k layer 254 can be etched to forminterconnect openings followed by removal of the patterned photoresistlayer and the hard mask layer. The portions of ESL 252 underlying theetched portions of low-k layer 254 can be etched to expose top metalcapping layers 250A-250C.

In some embodiments, prior to the blanket deposition of barrier layers256, a cleaning process using reactive H₂ ions/radicals can be performedon the interconnect openings to remove any residue (e.g., polymericresidue) from previous process steps (e.g., formation of interconnectopenings). In some embodiments, the blanket deposition of barrier layers256 can include depositing a first nitride layer (e.g., TaN layer) byALD with a thickness ranging from about 0.5 nm to about 1.5 nm, a secondnitride layer (e.g., TaN layer) by PVD with a thickness ranging fromabout 0.5 nm to about 1.5 nm, a metal liner (e.g., Co liner) by CVD witha thickness ranging from about 1 nm to about 3 nm, and a metal seedlayer (e.g., Cu seed layer) by PVD with a thickness ranging from about 1nm to about 2 nm. The first nitride layer can be blanket deposited byALD using reaction gases, such as PDMAT and NH₃ as precursors at atemperature ranging from about 200° C. to about 350° C. The secondnitride layer can be blanket deposited by PVD with Ta target andreaction gases, such as NH₃ at a temperature ranging from about 20° C.to about 40° C.

The blanket deposition of conductive lines 258 can include depositingconductive materials such as, W, Al, Co, or Cu using any suitabledeposition process, such as PVD, CVD, ALD, molecular beam epitaxy (MBE),high density plasma CVD (HDPCVD), metal organic (MOCVD), remote plasmaCVD (RPCVD), plasma-enhanced CVD (PECVD),electro-chemical plating (ECP),other suitable methods, and/or combinations thereof. In some embodiment,the blanket deposition of conductive materials can include ECP Cuplating on barrier layers 256 to fill interconnect openings. In someembodiments, conductive lines 258 can have a horizontal dimension (e.g.,width) along an X-axis ranging from about 20 nm to about 25 nm. In someembodiment, conductive lines 258 can have an aspect ratio ranging fromabout 2 to about 3, where the aspect ratio can be a ratio of theirvertical dimensions (e.g., height) along a Z-axis to their horizontaldimensions (e.g., width) along an X-axis. The CMP process cansubstantially coplanarize top surfaces of low-k layer 254 and theblanket deposited materials for barrier layers 256 and conductive lines258 to form interconnect structures 257A-257C, as shown in FIG. 2.

The present disclosure provides example structures and methods forreducing resistivity of via contact structures (e.g., via contactstructures 247A-247C) of semiconductor devices (e.g., semiconductordevice 100) using dual metal capping layers (e.g., bottom and top metalcapping layers 246A-246C and 250A-250C). The dual metal capped viacontact structures can be formed without barrier layers and can reducethe contact resistance interconnect structures and S/D contactstructures, gate structures and high R structures from about 10% toabout 30%, thus resulting in higher drive currents in the semiconductordevices with improved device performance. The top metal capping layerscan also prevent electromigration of metals from interconnect structuresto underlying structures to improve yield of the semiconductor devices.

The example structures and methods provide dual metal capped via contactstructures 247A-247C with substantially void-free via contact plugs248A-248C and bottom and top metal capping layers 246A-246C and250A-250C. The substantially void-free dual metal capped via contactstructures 247A-247C can be formed with low resistivity in via contactopenings 962A-962C with dimensions (e.g., width or diameter) from about10 nm to about 15 nm and with aspect ratio from about 5 to about 8.

In some embodiments, a method of fabricating a semiconductor deviceincludes forming a fin structure on a substrate, forming a source/drain(S/D) region on the fin structure, forming a gate structure on the finstructure and adjacent to the S/D region, forming and S/D and gatecontact structures on the S/D region and the gate structure,respectively. The forming of the S/D and gate contact structuresincludes forming S/D and gate contact plugs, respectively. The methodfurther includes forming first and second via contact structures on theS/D and gate contact structures, respectively, and forming first andsecond interconnect structures on the first and second via contactstructures, respectively. The forming of the first and second viacontact structures includes forming a first via contact plug interposedbetween first top and bottom metal capping layers and a second viacontact plug interposed between second top and bottom metal cappinglayers, respectively. The first and second via contact plugs havematerial compositions different from material compositions of the firstand second top and bottom metal capping layers. The first and secondinterconnect structures have material compositions different from thematerial compositions of the first and second via contact structures.

In some embodiments, a method of fabricating a semiconductor deviceincludes forming a transistor on a substrate, forming a passive deviceon the substrate and adjacent to the transistor, forming a contactstructure on the transistor, forming first and second via contactstructures on the contact structure and the passive device,respectively. The forming of the first and second via contact structuresincludes forming the first and second bottom metal capping layers on thecontact structure and the passive device, respectively, forming thefirst and second via contact plugs on the first and second bottom metalcapping layers, respectively, and forming the first and second top metalcapping layers on the first and second via contact plugs, respectively.

In some embodiments, a semiconductor device includes a fin structure ona substrate, a source/drain (S/D) region disposed on the fin structure,a gate structure disposed on the fin structure and adjacent to the S/Dregion, S/D and gate contact structures disposed on the S/D region andthe gate structure, respectively, first and second via contactstructures disposed on the S/D and gate contact structures,respectively, and first and second interconnect structures disposed onthe first and second via contact structures, respectively. The S/D andgate contact structures includes S/D and gate contact plugs,respectively. The first and second via contact structures includes afirst via contact plug interposed between first top and bottom metalcapping layers and a second via contact plug interposed between secondtop and bottom metal capping layers, respectively.

It is to be appreciated that the Detailed Description section, and notthe Abstract of the Disclosure, is intended to be used to interpret theclaims. The Abstract of the Disclosure section may set forth one or morebut not all exemplary embodiments contemplated and thus, are notintended to be limiting to the subjoined claims.

The foregoing disclosure outlines features of several embodiments sothat those skilled in the art can better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theycan readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they can make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A semiconductor device, comprising: a finstructure on a substrate; a via contact structure on the fin structure,wherein the via contact structure comprises a via contact pluginterposed between a first metal capping layer and a second metalcapping layer, and wherein the via contact plug has a materialcomposition different from that of the first and second metal cappinglayers; and an interconnect structure on the via contact structure. 2.The semiconductor device of claim 1, wherein the first and second metalcapping layers have a same material composition.
 3. The semiconductordevice of claim 1, wherein the interconnect structure has a materialcomposition different from that of the via contact structure.
 4. Thesemiconductor device of claim 1, further comprising: a source/drain(S/D) region on the fin structure; and a S/D contact structureconnecting the S/D region to the via contact structure.
 5. Thesemiconductor device of claim 4, wherein the S/D contact structure has amaterial composition different from that of the via contact plug.
 6. Thesemiconductor device of claim 1, further comprising: a gate structure onthe fin structure; and a gate contact structure connecting the gatestructure to the via contact structure.
 7. The semiconductor device ofclaim 6, wherein the gate contact structure has a material compositiondifferent from that of the via contact plug.
 8. The semiconductor deviceof claim 1, further comprising: a passive device on the substrate andadjacent to the fin structure; an additional via contact structure onthe passive device, wherein the additional via contact structurecomprises an additional via contact plug interposed between a thirdmetal capping layer and a fourth metal capping layer, and wherein theadditional via contact plug has a material composition different fromthat of the third and fourth metal capping layers; and an additionalinterconnect structure on the additional via contact structure.
 9. Thesemiconductor device of claim 1, wherein the via contact plug comprisesruthenium, the first and second metal capping layers comprise tungsten,and the interconnect structure comprises copper.
 10. A semiconductordevice, comprising: a transistor on a substrate; a device contactstructure connected to the transistor; a via contact structure on thedevice contact structure, wherein the via contact structure comprises avia contact plug interposed between a first metal capping layer and asecond metal capping layer, and wherein the via contact plug has amaterial composition different from that of the first and second metalcapping layers; and an interconnect structure on the via contactstructure.
 11. The semiconductor device of claim 10, wherein the firstand second metal capping layers have a same material composition. 12.The semiconductor device of claim 10, wherein the interconnect structurehas a material composition different from that of the via contactstructure.
 13. The semiconductor device of claim 10, wherein the viacontact structure has a material composition different from that of thedevice contact structure.
 14. The semiconductor device of claim 10,wherein the transistor comprises a source/drain (S/D) region, andwherein the S/D region is connected to the interconnect structure viathe device contact structure and the via contact structure.
 15. Thesemiconductor device of claim 10, wherein the transistor comprises agate structure connected to the interconnect structure via the devicecontact structure and the via contact structure.
 16. A method offabricating a semiconductor device, the method comprising: forming a finstructure on a substrate; forming a via contact structure on the finstructure, wherein the via contact structure comprises a via contactplug interposed between a first metal capping layer and a second metalcapping layer, and wherein the via contact plug has a materialcomposition different from that of the first and second metal cappinglayers; and forming, on the via contact structure, an interconnectstructure with a material composition different from that of the viacontact structure.
 17. The method of claim 16, wherein the forming thevia contact structure comprises: forming the first metal capping layeron the fin structure; forming the via contact plug on the first metalcapping layer; and forming the second metal capping layer on the viacontact plug.
 18. The method of claim 17, wherein the forming the viacontact plug comprises: removing a surface oxide from a top surface ofthe first metal capping layer to form a substantially oxide-free topsurface of the first metal capping layer; and depositing a metal of thevia contact plug on the substantially oxide-free top surface of thefirst metal capping layer.
 19. The method of claim 18, wherein theremoving the surface oxide from the top surface of the first cappinglayer comprises performing an argon plasma etch on the top surface ofthe first metal capping layer.
 20. The method of claim 17, wherein theforming the second metal capping layer comprises: etching back the viacontact plug; removing a surface oxides from a top surface of the viacontact plug to form a substantially oxide-free top surface of the viacontact plug; and depositing a metal of the second metal capping layeron the substantially oxide-free top surface of the via contact plug.